1. Field of Invention
The present invention relates to a flash memory device, and more particularly, to a universal serial bus flash memory integrated circuit that is connectable via a universal serial bus.
2. Description of Related Art
Flash memory has become an important means for storing data for the advantage of high mobility and non-erasable. This is an extremely useful way of storing data for portable devices such as handheld devices. The convenience that flash memory provides gives it numerous advantages over traditional mass storage devices such as hard disks. Besides portability, flash memory further offers advantages such as low power consumption, reliability, small size and high speed.
Flash memory is non-volatile which means that it retains its stored data even after power is turned off. This is an improvement over standard random access memory (RAM), which is volatile and therefore looses stored data when power is turned off.
Universal serial transmission interface is the standard of PC/NB/IA products. PC/NB/IA products are bootable by storage medium of serial transmission interface, thereby increasing the possibility of substituting serial transmission interface storage medium for hard diskdrive. Due to external attachment arrangement, existing serial transmission interface storage media cause certain inconveniences.
In order to fit different function requirements, current small-sized IA products, such as PDA, industrial computer, digital camera, and the like are commonly provided with an operation system, for example, Win CE/Linux. The hardware architecture requires a CPU and a NOR type flash memory for storing program code. If it is necessary to store data, SRAM or built-in NAND flash memory, or external memory card is needed. The aforesaid three measures are not of standard interface to Win CE/Linux. The designer needs to modify the driving program or application program of these operation systems. Therefore, it requires much effort and money on these interfaces when developing a new product.
As the number of mobile, portable, or handheld devices grows, the popularity of flash memory increases. The most common type of flash memory is in the form of a removable memory card. This card allows the contents of the flash memory to be transferred easily between devices or computers.
However, when moving the flash memory card between devices, an additional host or adapter is required in order for the host to communicate with the flash card. Many devices may not have the built-in ability to connect to a flash card, therefore a special adapter or card must be installed in the host device. In addition, the bus architecture can limit the speed of data transfer between the host and flash memory device.
Therefore, there is a need for a flash memory device that can be directly connected to a host device without the need for special cables or adapters.
To achieve these and other advantages and in order to overcome the disadvantages of a conventional flash memory card in accordance with the purpose of the invention as embodied and broadly described herein, the present invention provides a flash memory integrated circuit device that is connectable to a host via a universal serial bus.
The universal serial bus (USB) has become a standard serial interface, which allows data to be stored in and read from an external memory device at high speed. Therefore, it is advantageous to combine the benefits of a flash memory device with the speed of the universal serial bus. In addition, by designing the flash memory device with a USB interface, the flash memory device appears as a standard USB storage device, which permits the host and flash memory device to connect and interact with ease.
The main board of the flash memory integrated circuit device comprises a controller and at least one flash memory chip. A USB connector connects the flash memory integrated circuit device with a USB host. The flash memory on the main board comprises at least one flash memory chip but as described below, the memory capacity of the flash memory device can be easily expanded.
In an embodiment of the present invention, the memory storage device further comprises an extension stack connector that allows for extending the number of flash memories on slave boards. The extension stack connector connects the pins needed by the flash memory chip on the slave board with the controller on the main board. In this way, the memory capacity of the flash memory device can be conveniently expanded as required.
The controller is a major component of the device. The controller controls commands and data between the USB host and manages data in the flash memory array or module. It is preferred that the controller is of a single chip design that does not need external ROM or RAM.
A regulator regulates the voltage for the memory storage device. Typically, flash memory requires 3.3 volts or 5.0 volts. Some flash memory devices utilize means of switching between 3.3 volts and 5.0 volts as required by the flash memory. However, an advantage of the flash memory device of the present invention is that the flash memory device only needs 3.3 volts. Therefore, regardless if 5.0 volts or 3.3 volts is received from the host, the regulator will ensure that 3.3 volts is available for the USB transceiver without the need for detecting and converting the voltage.
A clock generator, for example a crystal, generates a clock signal for the controller of the flash memory device.
The flash memory integrated circuit device of an embodiment of the present invention further comprises an indicator, for example an LED indicator, which indicates the status of the memory storage device such as whether it is busy or in standby.
The main board of the flash memory device can also have a stack connector for connecting a slave board to the main board for extending the memory size with flash memory arrays. The slave board comprises at least one additional flash memory module or array. Multiple slave boards can be connected in order to provide unlimited memory expansion.
A write protection switch provides write protection from the USB host. The switch has at least two positions; a position for allowing the host to read and write normally, and another position for write protection. When the switch is in the write protect position, the host can read data but cannot write or erase data.
The controller of the flash memory device of the present invention performs numerous functions. Among these functions is controlling the USB interface. The controller follows the USB specification for physical and logical protocol. The controller further comprises a FIFO controller buffer. The controller receives command and parameter packets from the USB host, which are then stored in a special register defined by the controller. The controller is also responsible for controlling the transfer of data to and from the USB host. In addition, the controller also provides status data to the USB host.
When the host sends a write command, an interrupt is generated and sent to the controller microprocessor to inform the microprocessor of the command and the command location. The microprocessor, for example an 8 or 16-bit microprocessor, is a major component of the controller. The microprocessor reads the USB commands and parameters from the register. The microprocessor also executes the commands with parameters. The microprocessor manages and maps the USB FIFO address to the controller buffer while receiving or transferring data to and from the USB host. Also, the microprocessor manages commands such as erase, program, or read for the flash memory array. In addition, the microprocessor executes the addressing method according to the algorithm of the controller.
Microprocessor ROM stores the program code of the controller and is built into the controller. Microprocessor RAM is a system RAM used by the controller when executing USB commands or the flash algorithm. By eliminating the requirement for off-chip memory, the system cost is reduced.
A system buffer is used as a cache, which is provided for buffering between the USB interface and the flash memory array interface. It is also the FIFO of the USB protocol and the direction map to the buffer. The microprocessor manages the addresses of this buffer. As required, the buffer can be accessed by byte or word.
The flash memory integrated circuit device of the present invention further comprises a hardware state machine for creating the read and write timing to the system buffer between the USB host and the flash memory. A flash interface and circuit, controls the read and write commands to the flash memory array. In an embodiment of the present invention this is a pure hardware circuit.
In addition, an ECC circuit encodes the ECC code while data is writing to the flash memory array from the buffer cache and decodes the ECC code while data is read from the flash memory array to the buffer cache. If an ECC error occurs, the ECC circuit will determine the word or byte address in the buffer cache and correct the error.
The USB command implementation comprises the controller receiving commands and parameters from the USB host and storing them in a register defined by the controller. An interrupt is generated and sent to inform the microprocessor that a command has been received.
The controller receives and transfers data to and from the USB host according to the USB logical and physical specification. The addressing method comprises managing the flash memory erase, read, and write commands and manages the physical to logical mapping.
When the USB Host writes a command and parameter to the memory storage device, the controller will store it in a specified register. The data will then be read by the microprocessor as information from the USB host. According to the standard USB specification, the request parameter comprises 7 bits as shown in FIG. 5. Bits D6-D5 of the bmRequest Type designate the type of command protocol. The types include standard, class, and vendor. The flash memory device of the present invention supports all three of these types of protocols. The standard type is the standard device request, which is a common command such as USB_Get_Status or USB_set_Feature.
An embodiment of the flash memory integrated circuit device of the present invention utilizes the USB mass storage class with the bulk/control/interrupt transport.
Due to the physical limit of the flash memory, before the write command can be performed, an erase command must be executed first. Typical flash memory can function normally only until being erased about one million times, so minimizing the erase steps to maximize the flash memory""s usage life is very important. Therefore, the present invention provides a link table and a mother/child framework to achieve this aim.
Following is a description of the use of the link table. When initializing flash, all blocks are searched and a record of the relationship between the physical and logical block that the search has found, becomes the link table. At the same time, the unused physical blocks are put into the spare region for the FIFO queue to use. Next, the logical block in the Link Table is used to find the corresponding physical block address. By doing so, data associated with a particular physical block can accurately be written or retrieved.
When writing data to the flash memory, an erased block (new block) may need to be taken to replace an old block. Then data is written into the new block. Finally, the data, which has been not changed, is moved from the old block to the new block. This completes the action of writing a page""s data.
If multiple pages of data are to be written, the above steps are repeated. However, if data is repeatedly written into the same block, many unnecessary erase and move actions are performed. This not only wastes time but also reduces the lifetime of the flash. Therefore, in the flash memory device of the present invention, the erase action is avoided when repeatedly writing data to the same block and the move action is performed only when changing blocks. By using this method, not only is the lifetime of the flash increased but the efficiency of the device is also increased.
Following is a write data example. 32 sectors of data are to be written to flash which starts at block/page 0/0. The total physical block/logical block is 1024/992. The total spare blocks for the FIFO is 32. No blocks are defective. There are 32 pages per block. Child block number 03E0h, which is pointed to by the head pointer is taken from the FIFO spare region. The head pointer is then incremented and 32 pages of data are programmed into the child block. Child block number 03E0h is filled into the mother block""s logical block address 0000h in the link table. Mother block 0000h is erased and the tail pointer is incremented. Then, mother block number 0000h is filled into the tail pointer point address in the spare region.
Following is a description of a write procedure according to an embodiment of the present invention.
The host writes the corresponding write command and the address parameter to the memory storage device which then begins execution of the program flash algorithm. Then, the logical address from the USB host is converted to the flash memory physical block and page address. The controller checks to see if a child block exists.
If a child block doesn""t exist, a clean block is taken from the FIFO queue to create a child block for the current write command. Then, the current flash memory logical page number is checked to see if what is to be written is equal to xe2x80x9c0xe2x80x9d or not. If equal to xe2x80x9c0xe2x80x9d, the data from the host to the flash memory is programmed into the buffer and the sector count number is decremented. This process is repeated until the sector count number is equal to xe2x80x9c0xe2x80x9d. If what is to be written is not equal to xe2x80x9c0xe2x80x9d, the data from the mother block (which is clean) is moved to the child block between the sections xe2x80x9clast page writtenxe2x80x9d and the xe2x80x9ccurrent write pagexe2x80x9d. Then, the data from the host to the flash memory is programmed into the buffer and the sector count number is decremented. This process is repeated until the sector count number is equal to xe2x80x9c0xe2x80x9d.
If a child block exists, the current flash memory""s logical block is checked to see if what is to be written is equal to the last flash memory logical block that was written. If it is not equal, the data from the mother block is moved to the child block between the sections xe2x80x9clast page writtenxe2x80x9d and the xe2x80x9cend page of this blockxe2x80x9d. Then, the mother block is erased. The link table in the controller is updated substituting the original mother block address with the child block address. Then, the erased mother block is put back into the FIFO queue as a clean block. If what is to be written is equal to the last flash memory logical block that was written, the current flash memory logical page number is checked to see if what is to be written is larger than the last flash memory logical page that was written. If it is larger, the current write page number is checked to see if it is equal to the last page written plus 1. If yes, the data from the host to the flash memory is programmed into the buffer and the sector count number is decremented. This programming process is repeated until the sector count number is equal to xe2x80x9c0xe2x80x9d. If the current write page number is not equal to the last page written plus 1, the data from the mother block (which is clean) is moved to the child block between the sections xe2x80x9clast page writtenxe2x80x9d and the xe2x80x9ccurrent write pagexe2x80x9d.
If what is to be written is not larger than the last flash memory logical page that was written, the data from the mother block is moved to the child block between the sections xe2x80x9clast page writtenxe2x80x9d and the xe2x80x9cend page of this blockxe2x80x9d. Then, the mother block is erased. The link table in the controller is updated substituting the original mother block address with the child block address. Then, the erased mother block is put back into the FIFO queue as a clean block.
If what is to be written is larger than the last flash memory logical page that was written, the data from the mother block is moved to the child block between the xe2x80x9clast page writtenxe2x80x9d and the xe2x80x9ccurrent write pagexe2x80x9d sections. The data from the host to the flash memory is programmed into the buffer and the sector count number is decremented. The data is programmed until the sector count number equals zero.
For a read procedure of the flash memory device according to an embodiment of the present invention, the logical address from the USB host is converted to the flash memory physical block and page address. Then, the current flash memory logical block is checked to see if what is to be read is equal to the last flash memory logical block that was read. If no, the data from the flash memory physical block and page is read and the sector count number is decremented. This process is repeated until the sector count number equals xe2x80x9c0xe2x80x9d. If what is to be read is equal to the last flash memory logical block that was read, the current flash memory logical page is checked to see if what is to be read is larger than the last flash memory logical page that was written.
If yes, the data from the flash memory physical block and page is read and the sector count number is decremented. This process is repeated until the sector count number equals xe2x80x9c0xe2x80x9d. If what is to be read is not larger than the last flash memory page that was written, the data from the child block physical block and page is read and the sector count number is decremented. This process is repeated until the sector count equals xe2x80x9c0xe2x80x9d.
When the microprocessor begins to execute the command, the device will download its parameters from the host, for example, read or write, the vendor command packet. The system will judge the address mode by bit 6 of the Device/Head byte. The flash memory device of the present invention supports both the logical block address (LBA) and the cylinder head sector (CHS) mode. If the host provides the address using LBA mode, the device will convert it into CHS mode and then change the CHS mode into the physical address.
When the device executes a read command, the controller will first read data from the flash memory, sector by sector to a buffer (512 bytes) in the controller, then this sector will be sent to the host by a USB engine. The whole command will be completed when the number of sectors that have been sent to the host is equal to the sector count.
When the device executes a write command, the controller will read data from the host by the USB engine sector by sector to a buffer (512 bytes) in the controller, and then this sector will be stored in the flash memory. The whole command will be completed when the number of sectors that have been sent to the flash memory is equal to the sector count.
The device can support more than one piece of flash memory. In the present invention, multiple chip select pins are provided. When the device is initialized, it will check the type of the flash (the capacity) being used on board and how many chips the system has and the device will add up all the memory chips to find out the total capacity. When the host needs this kind of data, the device will provide the total capacity to the host, not just the capacity of one chip.
When the host sends a certain address (logic) to the device, the device will perform a calculation to find the exact chip and corresponding address that the host wants to access. Then the device will use the calculated address and enable the chip select pin.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.